This invention relates to position determination systems, in particular an apparatus for determining direction and heading. Specifically, the present invention pertains to a method for using such an apparatus to determine the amount of drift based on direction and heading measurements.
Satellite positioning system (SATPOS) devices that determine position using the satellites of the US Global Positioning System (GPS) are commonly Used for navigation of vessels, vehicles, airplanes, and other such crafts and conveyances. SATPOS devices are also used for surveying, construction site planning and management, mining, oil and gas exploration and development, etc. Also, handheld SATPOS devices are used for personal navigation, data collection, data maintenance, etc.
SATPOS devices are quite effective for indicating the position of the SATPOS device. Position is typically indicated using either an alphanumeric indication of position or by displaying a map that indicates position. Alphanumeric indications of position typically include coordinates such as, for example, latitude and longitude, World Geodetic Survey (WGS) coordinates, etc.
Map displays typically indicate position by an icon or other indicator visible on a map. One such map display, typically referred to as a moving map display, displays the position of the SATPOS in the center of the displayed map. Such map displays typically are oriented such that the top of the SATPOS device""s display indicates North (either magnetic North or true North). That is, irrespective of the direction in which the SATPOS device is actually oriented, North is shown at the top of the display. For users that intuitively know which direction is North, such maps are adequate for locating features displayed on the map. However, for users that do not know where North is, or when visibility is obscured such that the user cannot determine where North is, such maps are inadequate for guiding the user to a destination or feature on the map.
For many commercial applications of SATPOS systems, such as construction site planning and management, surveying, navigation, etc., it is essential that an operator be able to locate features displayed on the map. Such users typically operate a separate device for indicating direction such as a conventional magnetic compass.
Some SATPOS devices indicate the direction of movement of the SATPOS device, typically referred to as xe2x80x9cheading.xe2x80x9d Typically, heading is determined by analysis of determined position in relation to prior determinations of position as the SATPOS moves. Typically, SATPOS devices that indicate heading use a map display oriented such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to North (either magnetic North or true North).
Some prior art SATPOS devices orient the displayed map such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to the direction of movement calculated by the SATPOS device. This gives a good approximation of the user""s heading as long as the user continues to move and as long as the SATPOS unit is oriented in the direction of movement, allowing a user to easily determine the location of features visible on the display.
However, when the SATPOS device stops moving, determination of heading can no longer be made. Some SATPOS systems maintain the previous heading for orienting the moving map display for a given time interval. Other prior art SATPOS systems default to positioning North at the top of the map. This can be quite confusing to the user.
Recently, digital compasses have been developed that can indicate direction. However, digital compasses must be calibrated to properly align the digital compass prior to use. Also, each time that magnetic environment around the compass changes, the digital compass must be recalibrated. Digital compasses are typically calibrated by moving the digital compass in a full horizontal arc. The calibration process takes time and is prone to operator error. Also, calibration error can occur as a result local magnetic anomalies.
What is needed is a method and apparatus for providing an accurate indication of heading to a user of a SATPOS device. Also, a method and apparatus are needed that meet the above need and that accurately indicate direction when the SATPOS is not moving. Also, a method and apparatus are needed that are easy to use and that do not require a user to manually calibrate a compass.
As described above, a SATPOS device can be used for navigation of vessels, vehicles, airplanes, and other such crafts and conveyances. The SATPOS device can be used to determine the position of the craft and an approximation of the craft""s heading. A digital compass can be used to determine the craft""s direction.
However, a problem with navigating the craft occurs when the craft is caused to drift from its planned course. For example, consider a boat attempting to travel due North across a body of water. The boat""s driver will keep the bow of the boat pointing North according to the digital compass. However, the boat will be subject to tides, currents and winds that cause it to drift sideways from its intended course, even though the bow is still pointed North. The driver will believe he or she is proceeding due North, when in actuality the boat will also be drifting some amount to the East or West. Consequently, it is likely that the intended destination will be missed, even though the driver thinks he or she is on course.
The driver may use a SATPOS device to determine position and heading. However, as described above, some SATPOS devices indicate heading using a map display that is oriented such that the top of the SATPOS device corresponds to North, while other SATPOS devices orient the displayed map such that the top of the SATPOS device corresponds to the direction of movement calculated by the device. In the example above, the boat""s driver believes he or she is heading one direction (e.g., due North) when the boat""s drift is actually carrying the boat in a different direction. Thus, the SATPOS device may not be properly oriented, or the heading information may be misleading or confusing.
Furthermore, though the factors that cause drift (e.g., wind, current, etc.) are generally always present, the amount of drift that these factors can induce can vary significantly with time and location. For example, the velocity and direction of the wind velocity can change significantly with time, and currents can vary with location. Therefore, the magnitude and direction of drift will not be constant. As a result, multiple course corrections will be required. Each time, the driver or pilot must obtain position and heading information, compare it to the planned course and heading, and calculate the amount of drift. These tasks may be difficult and burdensome for a boater or pilot. In addition, these tasks may need to be performed frequently under those circumstances (e.g., high winds, strong currents, etc.) that can cause the craft to drift far off course unless frequent course corrections are made.
Accordingly, what is also needed is a method and/or system that can be used for accurate navigation accounting for factors such as drift. What is also needed is a method and/or system that accomplishes the above need and is also convenient and user-friendly. The present invention meets this need and the above needs.
The present invention provides a method and apparatus that accurately indicate direction and heading to a user of a satellite positioning system (SATPOS) device. The present invention also provides a method and system for determining an amount of drift based on the direction and heading information. The present invention is also user-friendly and convenient.
An integrated position and direction system is disclosed that includes a SATPOS having a receiver adapted to receive satellite position determining signals. The integrated position and direction system of the present invention also includes a digital compass that is adapted to determine direction.
The integrated position and direction system also includes a controller for controlling the operations of the integrated position and direction system. The controller is coupled to the SATPOS, the digital compass, and to a display.
In one embodiment of the present invention, when the SATPOS is moving, the direction of movement or xe2x80x9cheadingxe2x80x9d determined by the SATPOS is indicated on the display. When the SATPOS is not moving, the direction given by the digital compass is indicated on the display. Therefore, while the SATPOS is moving, the heading is indicated, and when the SATPOS is not moving, direction is indicated using the digital compass. Thus, the present invention provides a method and apparatus for providing an accurate indication of both heading and direction to a user of a SATPOS device.
In one embodiment, the digital compass is automatically calibrated by the SATPOS when the SATPOS is moving. This calibration can be initiated by the user or can be fully automatic. More particularly, the digital compass of the present invention is calibrated automatically, either as a result of user input (e.g., selection of an icon, pressing of a button, etc.), or as a result of user-defined criteria for automatic calibration. That is, the user can program the present invention to automatically calibrate the digital compass (e.g., when velocity exceeds a given threshold, whenever the SATPOS begins moving, periodically while the SATPOS is moving, when the difference between the SATPOS determined heading differs from the heading indicated by the digital compass by more than a predetermined threshold, etc.). Thus, the position and direction system of the present invention is easy to use because there in no need for a user to calibrate a compass as is required using a prior art compass alone.
In another embodiment, a method and system for determining drift using an integrated position and direction system are disclosed. The satellite positioning system is used for determining position and heading, and the digital compass is used for determining direction. An amount of drift is determined using the heading and the direction. The amount of drift can be displayed to a user along with the position, heading and direction information.
Knowing the amount of drift, a course compensating for the drift can be determined. Thus, a craft (e.g., a boat, airplane, etc.) that has drifted from its planned course can be directed to a course that will allow it to reach its intended destination. In one embodiment, the integrated position and direction system can be coupled to a navigation control system for the craft.
In accordance with the present embodiment of the present invention, frequent (relatively continuous) measurements of the amount of drift (magnitude and direction) can be provided to a user. As such, the user (e.g., a driver of a boat, a plane""s pilot or auto pilot, etc.) can make multiple, relatively minor adjustments along the way to compensate for the drift. Thus, in accordance with the present invention, the craft will follow a more direct course to its intended destination, and thereby will reach its destination more quickly and efficiently.